On Mon, 07 Nov 2005 10:50:15 -0500, Jerry Avins wrote:

Eric Meurville wrote:

The rotor is excited by an external rotating magnetic field generator
composed of a 3-Phi coil and 3 PWM generators.

It seems that you can know the position of the magnetic field by
measuring the coil currents. A knowledge of the viscosity on the medium
that embeds the rotor and the velocity of the field should allow you to
calculate the power angle between the field and the magnet. If
accelerations are small enough, a static calculation will do. Otherwise,
the rotor's inertia will need to be accounted for.

What you have is essentially a synchronous motor. It must either spin at
the same rate as the magnetic field or stall. When spinning, the angle
between magnet and field must be less than 90 degrees.

Jerry

I think Jerry's on to a good idea. If you're using external coils to
excite it then you should have everything you need to measure it as
well. Whether there are other objects within the fields which may
interfere with the measurements may be an issue, but you may be able
to calibrate or sense those and work around them.

Depending on the amount of power involved I think this may preclude
the use of a Hall effect sensor, anyway, which I think was the next
best idea. If this thing is small, though, and you can't get closer
than 10mm a Hall effect device may not have worked, anyway.


Eric Jacobsen
Minister of Algorithms, Intel Corp.
My opinions may not be Intel's opinions.
http://www.ericjacobsen.org